The present invention relates to the manufacture of multi-layer stacks of adhesive backed sheets and, more particularly, to a system for the continuous manufacture of pads of repositionable adhesive-backed sheet products or laminates of permanently adhered sheets.
The development of low tack adhesives comprising inherently tacky polymeric microspheres and systems for applying such adhesives to paper sheets in a manner inhibiting transfer of the tacky microspheres from the sheet to another surface has led to a broad line of easily removable and repositionable products in pad form. The notes comprising these pads each typically has a narrow strip of adhesive along one edge which holds the note against the underlying note in the pad or on another flat surface to which the note may be adhered after removal from the pad. As is well known in the art, small pads of notes are cut from large master stacks of sheets which are zone coated with the adhesive, laid up to form a stack of the desired number of sheets, and the stack is cut with multiple longitudinal and transverse cuts to form the smaller individual pads.
It was also recognized early in the development of these note pads that conventional sheet stacking techniques and apparatus were unsuitable because of the presence of the adhesive coating on one side of the sheet, which essentially precludes any sliding movement between sheets as they are stacked. One system which was developed to accommodate vertical stacking of large sheets of paper having zone coated adhesive strips on one side is shown in U.S. Pat. No. 4,743,319. In this system, large rectangular paper sheets having the zone coatings facing upwardly are individually conveyed horizontally into a backstop on the far end of a stacking bay and then allowed to drop vertically downward atop the preceding sheet until a stack of a desired number of sheets has been built up. Although this system recognizes the difficulty in squaring a stack of sheets having an adhesive coating on one side and purports to avoid the problem by direct vertical stacking, it is believed that sheet alignment and the maintenance of stack squareness remains a problem wherever positive control of the sheet is lost in the stacking process.
The method and apparatus described in U.S. Pat. No. 5,209,810 provide a solution to the sheet control and stack alignment problems inherent in prior art systems used to lay up stacks of adhesive-backed sheets. In accordance with that invention, a continuous paper web having zone coated adhesive strips is continuously applied to a series of recirculating pallets, onto each of which a length of web corresponding to the length of pallet is applied as the pallets and webs are fed in end-to-end register through a nip roll. A synchronized knife severs the web along the abutting edges of adjacent pallets and each pallet receives an additional sheet with each recirculating passage through the lay up station.
The maintenance of positive control of the web until sheets are laid in precise position on the pallet to form a master pad or master stack is the key to successful operation of the system disclosed in the preceding patent. That system has been successfully operated to accurately lay up master stacks of large adhesive backed sheets on a continuous basis, which stacks may be cut into a multiplicity of small note pads in a known manner. It has been found, however, that the principle of continuous web control can be applied in an even more efficient manner to lay up large sheets of adhesive-backed paper material on a continuous basis.
Indeed, the system of the invention to be described herein is broadly applicable to the lay up of sheets of other web materials than paper, webs which are zone coated or provided with a full coat of adhesives which may be repositionable or permanent, and to produce layered sheet products which are intended to be taken apart or to be permanent laminates.